1. Field
The invention herein disclosed generally refers to mobile ad-hoc networks, and specifically to synchronization of time in a mobile ad-hoc network.
2. Description of the Related Art
A mobile ad-hoc network (MANET) is a wireless ad-hoc network that supports a dynamic topology. Any mobile node in a MANET may communicate with any other node, either directly or through multiple hops across the network topology. Clock synchronization in a MANET is important for providing optimum efficiency and network throughput. Additionally, synchronization may result in significant power savings.
Current protocols may provide network time to the nodes in a MANET. A commonly used protocol is NTP (network timing protocol) originally used to maintain clocks for computers attached to the Internet. In the context of a MANET where nodes operate autonomously and might not receive explicit synchronization or other timing information, other timing protocols have been developed. The most commonly used protocol is the Reference Broadcast Synchronization (RBS) protocol. This protocol requires many transmissions and time stamps exchanged between nodes to establish a local time reference. However, this is costly in terms of spectrum usage and processor needs.
Other protocols for enabling synchronization in MANETs are Lightweight Time Synchronization (LTS), Timing-sync Protocol for Sensor Networks (TPSN), Hierarchy Referencing Time Synchronization (HRTS) and the like. These protocols utilize dedicated network traffic and communication between the nodes, which can reduce network efficiency.
In existing protocols, a receiving node in a network resolves time and frequency offsets on each packet prior to demodulation. This includes resolving frequency offsets between the receiver and the received waveform due to oscillator error, Doppler Effect, and the like. The time and frequency offset resolution includes calculating frequency error after ensuring successful time acquisition. This information is passed to the timing protocol.
Another commonly used protocol uses an approach that includes broadcasting timing information by access points (APs) in the network to other nodes in the network. However, this process results in a timing error that is accumulated at each hop while communicating the timing information due to transit delays.
There remains a need for a method and system that synchronizes time between the nodes in a MANET without dedicated communications among MANET nodes. Additionally, there remains a need for synchronization techniques that reduce loading on network capacity.